1. Field of the Invention
The present invention relates to a printing device which has a function of correcting printed letters with good precision.
2. Description of the Prior Art
In order to correct a letter erroneously printed on a recording paper sheet, an ink of the same color as the recording paper sheet (normally, white) is applied to the letter which is then erased. A conventional correction method of this type will be explained with reference to FIG. 1. Letters, A, B, C, E and E are erroneously printed in a 5.times.7 dot matrix. The order of letters is supposed to be A, B, C, D and E. The fourth letter E must be corrected to D. For this purpose, all the dots which correspond to the letter E in the 5.times.7 dot matrix are coated with a white ink, as shown in FIG. 2. The dots which are indicated by cross-hatched lines correspond to erroneously printed letter E, while the dots indicated by hatched lines are coated with the white ink. FIG. 3A is a sectional view of the letter coated with the white ink on the recording paper sheet. The letter D is then printed with a black ink. In this correction method, the erroneously printed letter may not be corrected with high precision. The previously printed letter may be seen through the white ink layer. Especially, if a space is left blank after the letter is erased, that is, if a new letter is not printed thereon, the erroneously printed letter can be seen, resulting in poor appearance. Further, with the correction method of this type, the white ink may not be applied completely to cover the letter due to irregular carriage feeding. This irregular feeding occurs with changes in a drive voltage and deformation of the belt for driving the carriage. As shown in FIG. 3B, when this occurs, the white ink 1 is not properly applied to a letter printed with the black ink 2, resulting in great degradation of printing quality.